1. Field of the Invention
This invention is related to the general field and classification of molten metal dispensing, and to the more specific field of apparatus for unplugging a vessel discharge port with a telescoping thermal lance.
2. Description of Related Art
The use of a telescoping thermal lance to burn through an obstructing plug in the discharge port of a vessel containing molten metal is described in U.S. Pat. No. 4,450,986 to Harasym and Lanza; U.S. Pat. No. 4,746,037 to Harasym; and U.S. Pat. No. 4,877,161 to Harasym. Reference can be made to those publications, if needed, for background on the configuration and operation of such discharge ports, the causes of their blockage, and the general use of telescoping thermal lances to burn through the obstruction and initiate flow of the molten metal through the discharge port.
In U.S. Pat. No. 4,450,986, the telescoping lance assembly (identified by reference number 41 on its FIG. 1 and by number 61 on its FIG. 2) is a cylindrical housing that encloses a free floating hollow metal tube. High pressure oxygen (on the order of 100 psi) is ported through the housing to propel the tube upward into the obstruction and to sustain burning as the combustible material is ignited. The tube is partially filled with magnesium wires or low carbon steel wires as the primary combustible material
In U.S. Pat. No. 4,746,037, the telescoping lance assembly is essentially the same as in U.S. Pat. No. 4,450,986, except that the free floating tube has a flared bottom and a combustible collar at the top. The flared bottom is wider than the opening in a bushing located at the top of the housing to keep the tube from falling out of the housing if it is faced downward during handling or installation. The tube is filled with magnesium wires or low carbon steel wires intertwined with steel wool to allow oxygen flow and provide high surface area for combustion. The combustible collar is a cardboard sheath wrapped around a low temperature blasting fuse and the exposed ends of the wires and steel wool. It provides a more reliable ignition, among other things, over the U.S. Pat. No. 4,450,986 configuration.
U.S. Pat. No. 4,877,161 discloses an improved lance assembly in both the conventional telescoping mode and in a double telescoping mode to provide greater extension into a deep discharge port without needing to elongate the housing. The lance assembly (identified as 31 in its FIG. 1 and as 91 in its FIG. 11) again includes a cylindrical housing with a port to admit high pressure oxygen. Inside the housing is either one or two free floating tubes having a flared bottom. The tube (when single) or uppermost tube (when dual) contains combustible magnesium or low carbon steel wires as combustible material, and the tube is crimped into the wires at the top and bottom of the tube to prevent the wires from moving forward or backward inside the tube. As in U.S. Pat. No. 4,746,037, the tips of the wire extend out of the top end of the tube and they may be capped with an igniter covered by tape.
An unpatented variation of lance assembly that has come into the prior art since the publication of the three patents described above is shown in FIG. 1. The lance assembly 10 shown is a double telescoping type. The improvement was in the combustible lance 12. The telescoping tube 14 within the housing 16 is made of stainless steel to provide a lower rate of consumption than the more combustible material of the thermal lance 12 inside of it. The tube may have a flared base or a base flange 15 to keep it centered in the housing, and the housing may include a bushing near the top end to prevent the tube from completely exiting the housing. The combustible material of the lance is a combination of thin cylindrical rod 20 made of low carbon sheet metal that is roll-formed into a cylindrical rod that allows air to flow axially through the rod. Rods of this type, and the process of making them, are described in U.S. Pat. No. 4,787,142. They are used as electrodes in exothermal cutting of metal and are commonly called burner bars or slice rods. They can be obtained from welding supply channels of distribution under the brand ARCAIR. The axial air flow and increased surface area as compared to a solid bar or a hollow tubular bar provide rapid ignition and burning in the presence of high temperature and oxygen flow.
The rod 20 is surrounded by a low carbon steel sheath 22 to provide rigidity and more mass of combustible low carbon steel. The sheath 22 is formed to have an inner bore slightly greater than the outer diameter of the rod 20, and an outer diameter less than that of the stainless steel tube 14. A section of slice rod is cut to less than the length of the housing 16 to form the inner rod 20, and a section of sheath material is cut to a shorter length than the rod, such that the rod 20 can be inserted into the sheath 22 to extend about ¾ inch to 1½ inch beyond one end 24 of the sheath and several inches out of the other end 26. One end of the sheath 26 is welded to the rod 20 where the longer end of the rod extends, such that the rod 20 and sheath 22 move together as a combustible lance 12 within the telescoping tube. The top end of the tube 14 can be crimped into a shape like a bullet and filled with a steel wool (not shown) and a low temperature blasting fuse 32.
This later design of lance 12 provided greater combustible mass and more rigidity than the prior lances filled with steel or magnesium wires. Oxygen flow through the inner rod 20 and between the low carbon sheath 22 and the tube 14 provided burning over a large surface area near the tip of the lance 12, and the sheath 22 provided substantial rigidity to keep the combustible lance pushed into the obstruction in the discharge port without bending and provided a substantial amount of combustible material.